For bone treatment in general, a pinning device, as described in Patent Application n. TO94A000407 filed on May 20, 1994 by the present Applicant, is used comprising a cannulate metal rod, which is inserted inside the medullary canal of the bone; and an anchoring or pinning assembly for releasably connecting one or both end portions of the cannulate rod to respective portions of the bone.
The anchoring assembly comprises two or more deformable metal pins and, for each pin, a respective guide conduit formed inside the cannulate rod. Each conduit has an inside diameter approximately equal to but no smaller than the outside diameter of the respective pin, so as to guide the pin along a given path, and the pins are connected positively to a common slide, which is movable from the outside by means of a mechanical device for moving the pins simultaneously to and from a forward pinning position, in which respective deformed end portions of the pins project outwards from the rod and are inserted in use, inside the respective bone portion.
Though widely used, by permitting withdrawal of the pins from the bone when the fracture heals, known devices of the above type are not altogether satisfactory, mainly on account of the considerable force normally required to remove the pins.
This is substantially due to the inside diameter of each guide conduit being comparable with the outside diameter of the respective pin, so that, when withdrawing the pin, fairly severe friction components opposing withdrawal are generated between the pin and the conduit. For this reason, the pins are connected to said mechanical device, which not only increases the cost of producing the device, but, by comprising a single slide common to all the pins, also creates problems when, for various reasons, the pins must be withdrawn separately.
Moreover, the conduits of known devices of the above type are at times fairly difficult to form, due to their normally being formed by drilling and subsequently milling a solid portion of the rod.